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Development of mycorrhizal communities in primary succession
Mádle, Jan ; Kohout, Petr (advisor) ; Ponert, Jan (referee)
Primary succession is the process of ecosystem development that takes place in sites that were not suitable for colonization by plants and organisms dependent on them. These sites arise either naturally, for example after a volcanic eruption or glacial retreat, or anthropogenically, for example by strip mining. During primary succession, plants colonise the bare substrate and gradually modify its abiotic and biotic conditions. During primary succession, interactions between plants and the soil microbiome, especially with fungi and bacteria, occur. Plants and soil microorganisms influence each other's growth and development through various interactions. Plants, or rather their roots, form a specific niche for a wide range of soil microbial communities. Through their roots, plants provide a wide range of substances, organic acids, sugars, amino acids and other often carbon-rich compounds that can serve as a substrate for microorganisms. Plants are able to do this by producing litter, root exudates, and translocation of sugars for symbiotic fungi and bacteria. Soil microorganisms contri- bute to the release of nutrients and the decomposition of organic materials that would otherwise be unavailable to plants. Many soil microorganisms can form a symbiotic relationship with the plant; this relationship may be...
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Adaptations of epiphytic plants to water and nutrient uptake
Oppeltová, Soňa ; Ponert, Jan (advisor) ; Neuwirthová, Eva (referee)
Epiphytes are plants that grow on other plants but do not parasitize them. Because of irregular availability of water and nutrients, epiphytes evolved specific adaptations. These adaptations enable fast water and nutrient uptake and their efficient storage. For the uptake of water epiphytes evolved especially adaptations of roots and leaves. Roots produce velamen radicum and leaves develop specific absorptive trichomes. The uptake of water is related with the uptake of nutrients because first drops of rain are nutrient relatively rich. Another source of nutrients is organic material which falls from trees. Some epiphytes can retain it and acquire nutrients from its decomposition. Animals can also help epiphytes with nutrition. They can provide urea which is probably very essential for many bromeliads. Animals can also live in more specific symbioses with epiphytes, the most common being the symbiosis with ants. Epiphytes evolved many adaptations, but some of them are poorly understood.
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How will a longer vegetative season affect carbon sequestration in plant biomass
Kasperová, Denisa ; Albrechtová, Jana (advisor) ; Ponert, Jan (referee)
As a result of human activity, a large number of greenhouse gases, especially CO2, is released into the atmosphere, which causes a greater greenhouse effect and an increase in the temperature of the surface of the planet and the air in the atmosphere. Ongoing climate change is one of the great challenges facing society, as rising temperatures on the planet greatly affect the functioning of its ecosystems. Extremes arising from climate change, especially temperature rise and lack of precipitation or a change in the annual distribution of precipitation, affect the physiology and phenology of plants. Higher temperatures cause plant growing seasons to shift and lengthen, which has a direct impact on the sequestration of carbon in plant biomass through a biochemical, physiological plant process called photosynthesis. The increase in CO2 concentration in the atmosphere is slowed down by terrestrial forest ecosystems, as they can retain carbon in their tissues, especially in wood, for a relatively long time before it returns to the atmosphere. However, the efficiency of binding carbon into biomass also depends on other physiological processes, e.g., photorespiration, breathing, gas exchange between the plant and the atmosphere. Stressors caused by climate change can then limit growth, photosynthesis,...
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Mechanisms of physical dormancy and germination of orchid seeds
Jiroušková, Anna ; Ponert, Jan (advisor) ; Vosolsobě, Stanislav (referee)
Orchid seeds are called dust seeds because of very reduced structure. A mature dust seed is composed of living embryo and two seed coats which are formed by dead cells. While the outer seed coat is distinctive, the inner seed coat (known as carapace) is very thin and tightly surrounds the embryo. Seed coat is hydrophobic and prevents water from entering embryo. To induce germination artificially, calcium hypochlorite or sodium hypochlorite solutions are often used. However, the effect of chemical scarification on seed coats is poorly understood. I focused on seeds of Epipactis helleborine and Dactylorhiza majalis and I analysed changes in seeds induced by calcium hypochlorite treatment using germination of seeds in vitro, permeability tests of seed coats and histochemical analyses of selected components of seed coats. The most prominent change observed was decrease of amount of lignin in the outer seed coat. This is likely related to increase in permeability of seeds and stimulation of in vitro germination rate in Dactylorhiza majalis which has only thin and less complex inner seed coat. However, this relationship was less evident in Epipactis helleborine, which has thicker and more complex inner seed coat which is more resistant to hypochlorite scarification. This could indicate existence of...
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The phenomenon of Foliar Water Uptake - mechanisms and consequences with a focus on temerate plant species
Oramová, Viktorie ; Lhotáková, Zuzana (advisor) ; Ponert, Jan (referee)
The ability of plants to absorb water through leaves has been a matter of the sientific discussion for a long time. Among the epiphytic species (tilandsies for example), reduced root system and foliar water uptake (FWU) is considered an adaptation for life in soil-less environment, and FWU is a necesssity. It was surprising, that the same ability has been discovered in plant species with normally developed root system. Over the time, new pieces of evidence about FWU in broad range of plant species has been published and FWU is getting universal for all plants, across the taxonomic groups or biomes, including temperate zone. The systematic focus on FWU and continuity of its research is lacking and therefore the knowledge about FWU is still only partial. This bachelor's thesis is focused on mechanisms of FWU and the leaf structures that may mediate it. The ability of water to pervade cuticle through aquatic pores is discussed, together with the possibility of water absorption by stomata, trichomes, hydathodes or epiphylic organisms. Another discussed topic is the use of this water by plant - improving of the water regime, refilling of the embolized xylem vessels, possible exudation by roots etc. The matter of FWU has other consequences on the ecosystem level, like in water cycle or the plant's...
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Adaptations of orchid roots to epiphytism
Ungrová, Anna ; Ponert, Jan (advisor) ; Soukup, Aleš (referee)
The evolutionary success of orchids is to a large extent driven by the ability to colonize epiphytic habitats. This ability is based on a number of adaptations at different levels, and the adaptive features of aerial roots can play a key role because the roots are practically the only organ providing water and nutrient uptake. The main aim of this work is to review available information about roots of epiphytic orchids (Orchidaceae), especially their adaptations to the epiphytic way of life. The roots of epiphytes must deal with a periodic lack of water and nutrients, often in conjunction with high irradiation. The roots of epiphytic orchids adapt to these conditions on many levels. Rhizodermis forms a velamen capable to retain water and nutrients and protecting roots against environmental conditions including UV radiation. Root cortex contains chloroplasts, which can perform photosynthesis at least in some orchid species. Exodermis is well differentiated with thick secondary cell walls and acts as a selective barrier for the transport of substances with the use of passage and aeration cells. The function of some adaptive structures is still unclear, for example, tilosomes could regulate transpiration. Epiphytism evolved multiple times in orchids, and some root adaptations therefore originated...
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Ecophysiological relevance of extreme sensitivity of orchids to nitrates
Figura, Tomáš ; Ponert, Jan (advisor) ; Tylová, Edita (referee)
Many orchid species are seriously endangered at present. Reasons for their disappearing from natural habitats remain often unclear. Orchids depend on mycorrhizal symbiosis in nature, however only little is known about this symbiosis. Seeds of some species do not germinate in vitro, making their cultivation for scientific and rescue purposes impossible. We found that seed germination of one of such reluctant species, Pseudorchis albida, is strongly inhibited by nitrates even at extremely low concentrations. As this species prefers oligotrophic mountain meadows, nitrate-induced inhibition probably take place in natural conditions. Surprisingly, we found similar but slightly weaker inhibitory effect also in typical mesophillic species and even in slightly eutrophic ones. The sensitivity to nitrates correlates with trophy level of species canopy. This inhibitory effect of nitrates could be weakened by application of a range of growth regulators, including auxins, cytokinins and gibberellins, and also by mycorrhizal fungi. The action of nitratereductase is essential for this inhibitory effect of nitrates. Experiments with NO donors, scavengers, and NO quantification are pointing right at NO as compound which perhaps mediates nitrate inhibitory effect. Based on these results, the nitrate inhibitory...
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Emissions of isoprene by oil palm and their impacts on climate and composition of the atmosphere
Palouš, Daniel ; Albrechtová, Jana (advisor) ; Ponert, Jan (referee)
Biogenic volatile organic compounds (BVOC) serve many physiological and ecophysiological functions in plants, e.g. abiotic or biotic stress protection or signalling. Emission capacity and spectrum of emitted BVOC vary between plant species. Isoprene, having the highest global annual emission among all BVOC, has considerable influence on atmospheric chemistry and its processes. Isoprene contributes to secondary organic aerosol formation. Under specific conditions reaction of isoprene and NOx may lead to ground-level ozone formation. Isoprene also affects oxidative capacity of the atmosphere. Oil palm (Elaeis guineensis Jacq.) is a rapidly expanding crop and it is a strong isoprene emitter. Most of the global cultivation of oil palm is located in a relatively small region in southeast Asia posing a risk to regional air quality. To prevent ground-level ozone formation, keeping ground-level NOx concentrations low in the regions of oil palm cultivation is crucial. Models of global isoprene emission vary greatly and not all of them take oil palm cultivation in account. The present thesis aims to cover current knowledge on physiological functions of isoprene's synthesis and emission with regard to oil palm cultivation and ecological implications of mentioned processes. The thesis includes also brief...
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The role of trehalose in mycorrhizal associations
Šoch, Jan ; Ponert, Jan (advisor) ; Hála, Michal (referee)
Mycorrhizal symbiosis is a widely spread phenomenon in nature. A translocation of nutrients occurs between symbionts with disaccharide trehalose playing a key role in the process. However, this saccharide fulfils many important roles in metabolism of fungi and plants. Fungi use trehalose mainly as storage and transport saccharide. On the other hand, trehalose occurs in extremely low amounts in plants where it acts as a signal molecule. Thus it is likely that the saccharide could be used by the fungus to manipulate plant metabolism on a physical interface between symbionts. Trehalose has a similar function in many parasitic interactions. In most cases of mycorrhizal associations trehalose synthesis creates a carbon sink in mycelium which leads to saccharide transfer from the host plant to the fungus. Completely different situation occurs in the types of mycorrhizal symbiosis, where saccharides are translocated from a fungus to a plant. Some plants can utilize trehalose effectively as a sole source of energy. Consequently, the question raises - could such plants gain fungal trehalose on purpose as a source of energy and carbon? This review aims to assess and discuss the mentioned possibilities considering available literature. Key words: mycorrhiza, orchids, parazitism, saccharides, sink, symbiosis,...
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Mechanisms that control physiological seed dormancy
Řezková, Natálie ; Ponert, Jan (advisor) ; Vosolsobě, Stanislav (referee)
Physiological dormancy is an important developmental trait ensuring that seed does not germinate when the environmental factors are appropriate only temporary. The transition from seed dormancy to germination is regulated by a large number of factors and the phytohormone abscisic acid (ABA) plays a crucial role. Enhanced response to ABA and its biosynthesis is a key mechanism in dormancy induction and maintenance. ABA interacts antagonistically with gibberellins (GAs). Therefore GA biosynthesis and ABA catabolism are positive germination regulators. However, other phytohormones are also involved in the regulation of dormancy and germination. The most studied is ethylene which supports germination similarly to GA. Numerous factors affect dormancy at molecular level, namely chromatin remodeling, gene products that function only in dormancy regulation [e.g. DELAY OF GERMINATION 1 (DOG1)] or gene products that mediate seed response to environmental factors. The dormancy, its induction, depth and release, is driven not only by environmental conditions affecting mature seeds, but also by conditions acting during seed maturation in a maternal plant when the primary dormancy is induced. Requirements for dormancy release and germination induction may vary considerably between species. The physiological...
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